Biomedical subjects
Thomas J Walters
Publications and source records attributed to Thomas J Walters.
Effect of fluid resuscitation on acute skeletal muscle ischemia-reperfusion injury after hemorrhagic shock in rats.
BACKGROUND: Severe extremity wounds with vascular injury are common in military trauma, and tourniquets are commonly used for hemorrhage control. The complications of tourniquet use in the setting of trauma are not well studied. This study investigated the combined effect of hemorrhagic shock and fluid resuscitation with Hextend (HX; BioTime, Inc) or lactated Ringer's (LR) on skeletal muscle subjected to tourniquet-induced ischemia-reperfusion injury. STUDY DESIGN: Thirty male Sprague-Dawley rats underwent 33% arterial hemorrhage followed by 3 hours of tourniquet application. Before reperfusion, 10 animals each were resuscitated with lactated Ringer's (3 times shed volume) or HX (shed volume). Ten control animals received no resuscitation. Rats were euthanized 2 hours after tourniquet release and the tibialis anterior and medial gastrocnemius muscles were examined for edema (muscle wet weight) and viability (nitroblue tetrazolium reduction). Contralateral muscles served as controls for each animal, with results expressed as the ratio of the tourniquet limb to contralateral limb values. RESULTS: The tibialis anterior and medial gastrocnemius muscles in all groups experienced edema, with all weight ratios greater than one. Resuscitation with HX resulted in significantly (p < 0.05) greater edema than did no resuscitation in both muscles and greater edema than with lactated Ringer's in the medial gastrocnemius. All groups experienced a loss of viability as well, with nitroblue tetrazolium reduction ratios less than one. Resuscitation with HX resulted in significantly less viability loss than did no resuscitation in the medial gastrocnemius. No significant differences in viability were seen in the tibialis anterior. CONCLUSIONS: Resuscitation with HX or lactated Ringer's does not adversely affect muscle viability in ischemia-reperfusion injury. HX may be a better clinical choice when skeletal muscle ischemia-reperfusion injury is a risk, despite greater edema.
The role of epimysium in suturing skeletal muscle lacerations.
BACKGROUND: Direct muscle trauma is a common and disabling clinical problem. Surgical muscle repair is difficult to evaluate because reliable repair techniques have not been established scientifically. The purpose of this study was to assess the biomechanical properties of epimysium, the collagenous tissue sheath that surrounds muscles in the body. STUDY DESIGN: We surgically repaired transected porcine muscle bellies with and without epimysium. For both groups, 25 figure-eight stitches in lacerated quadriceps bellies from a euthanatized pig were loaded under tension on a biomechanical machine (model 8521S, Instron Company). Maximum loads and strains were measured and mechanisms of failure recorded. RESULTS: The mean load for repairs with epimysium (25.1 N) was significantly higher (p = 0.034) than that for repairs without epimysium (21.2 N). The mean strain for repairs with epimysium (10.4%) was significantly higher (p < 0.001) than that for repairs without epimysium (7.3%). The mechanisms of failure were also different. Among epimysium repairs, 15 stitches avulsed muscle transversely, and 10 stitches tore out longitudinally from the muscle. In the nonepimysium group, 1 suture avulsed muscle and 24 sutures tore out. Muscle was the weakest element in each test. CONCLUSIONS: These data showed that epimysium incorporation into suturing improves the capacity of repairs to bear force. These findings fill a knowledge gap and may improve outcomes of muscle suturing. By focusing the experiment on biomechanical properties of muscle stitching, this study showed the key role epimysium plays in muscle suturing.
Epimysium and perimysium in suturing in skeletal muscle lacerations.
BACKGROUND: Direct muscle belly trauma is common. Selecting optimal methods for surgical repair of muscle disruption is difficult because reliable methods have not been established. Suturing tendon offers strong repairs, but epimysium and perimysium, the connective tissues that coalesce to form tendons, offer unknown repair strength. The purpose of this study was to compare biomechanical properties of repaired muscle in transected muscle bellies with epimysium and perimysium. METHODS: The authors surgically repaired with figure-eight stitches in both epimysium and perimysium groups. Individual stitches were placed in lacerated quadriceps bellies from a euthanized pig and were tensioned on a biomechanical machine. Maximum loads and strains were measured, and failure mechanisms were recorded. RESULTS: Loads and strains for repairs with epimysium were higher than those for repairs with perimysium. Failure mechanisms were significantly different between groups. CONCLUSION: These data showed that epimysium incorporation into suturing improves capacity to bear forces compared with perimysium incorporation.
Issues related to the use of tourniquets on the battlefield.
On the battlefield, a properly applied tourniquet can be an extremely effective means of controlling severe extremity wound hemorrhage. However, a great deal of confusion exists among soldiers, medics, and military medical officers on a number of tourniquet-related issues. What is an appropriate combat tourniquet? When is it appropriate to use a tourniquet? When and by whom should a tourniquet be removed? Under what conditions should a tourniquet not be released or removed? What are the most effective ways to increase limb salvage while using a tourniquet? These and other issues were addressed by a panel of experts at the 2003 Advanced Technology Applications for Combat Casualty Care Conference, August 21 and 23, 2003, St. Pete Beach, Florida. Here we review those issues and present a summary of the panel's recommendations.
Physiological evaluation of the U.S. Army one-handed tourniquet.
OBJECTIVE: To provide a physiological assessment of the U.S. Army one-handed tourniquet (OHT). METHODS: An OHT was self-applied by 26 subjects, to maximal tolerable tightness, to the proximal arm or thigh under different conditions and positions, and the presence of blood flow was assessed using Doppler ultrasonography or occlusion plethysmography. RESULTS: Doppler sound was eliminated at the radial artery for all subjects with OHT application but was not stopped at the popliteal or dorsalis pedis artery for any subjects. The OHT reduced forearm blood flow by 79% but decreased leg blood flow by only approximately 50%, regardless of condition and position of application to the thigh. CONCLUSIONS: The OHT appears to effectively minimize blood flow in the arm but not in the lower extremities, and clinical assessment of blood flow disappearance by Doppler ultrasonography may underestimate the magnitude of actual blood flow to the limb.
Thermoregulation by rhesus monkeys at different absolute humidities.
The effect of relative humidity on thermoregulation has been well examined. Because the same relative humidity represents very different absolute humidities at different ambient temperatures, the present study was designed to examine the interaction of temperature and absolute humidity on the thermal balance of rhesus monkeys, Macaca mulatta. Thermal balance was examined in six unacclimated, unanesthetized, female rhesus monkeys at ambient temperatures of 25, 30, 35, and 40 degrees C and absolute humidities of 6, 22, and 40 torr. Monkeys were capable of achieving thermal balance under all conditions except at 40 degrees C with 40 torr absolute humidity, where experiments were stopped after rectal temperature exceeded 40.5 degrees C. At 40 degrees C, monkeys increased evaporative heat loss through both respiration and sweating; the slope of the relationship between evaporative heat loss and core temperature was attenuated by increases in absolute humidity. In contrast, absolute humidity had no direct effect on metabolic rate. The rise in body temperature under the conditions of high heat/high humidity was therefore most attributable to humidity-dependent decreases in evaporative heat loss.
Effects of blood flow on skin heating induced by millimeter wave irradiation in humans.
We have previously reported species differences in the rate of skin heating in response to millimeter wavelength microwave exposure. We hypothesized that these differences were predominantly a function of species differences in the ability to increase skin blood flow during local heating. Mathematical modeling also suggested that, in humans, the rate of skin heating during prolonged millimeter wavelength exposure would be dependent on skin blood flow. In order to empirically test this hypothesis, we determined the role of baseline skin blood flow on the rate of cutaneous heating induced by 94-GHz microwave energy in humans (3 female, 3 male) using infrared thermography and laser Doppler imaging to measure skin temperature and relative skin blood flow, respectively. Millimeter wavelength exposure intensities used were high power (HP), 1 W x cm(-2) for 4 s and low power, 175 mW cm(-2) for 180 s. Skin blood flow was (a) normal, (b) eliminated using a blood pressure cuff to occlude forearm blood flow, or (c) elevated by heating the skin prior to irradiation. Results showed that for the HP exposures, these manipulations did not influence the rate of skin heating. For the low power exposures, occlusion of baseline skin blood flow had a small impact on the subsequent rate of heating. In contrast, a two-fold elevation in baseline skin blood flow had a profound impact on the subsequent rate of heating, resulting in a substantially lower rate of heating. Occlusion of an elevated skin blood flow reversed this lower rate of heating. The results of these studies demonstrate that relatively small changes in skin blood flow may produce substantial alterations in the rate of skin heating during prolonged 94-GHz exposure.
Effectiveness of self-applied tourniquets in human volunteers.
BACKGROUND: Tourniquets are not commonly used in routine extremity trauma, but can be vital for hemorrhage control in austere conditions. OBJECTIVE: To determine the effectiveness in human volunteers of currently available self-applied tourniquets for extremity hemorrhage. METHODS: Seven tourniquets were tested on the thigh for elimination of detectable distal pulse by Doppler auscultation at the popliteal artery (experiment I, n = 18 subjects). The tourniquets that were effective in >or=80% of subjects in experiment I were tested for effectiveness on the upper arm by auscultation at the radial artery (experiment II, n = 12 subjects). RESULTS: Three of the seven tourniquets were effective in all subjects in experiment I; a fourth tourniquet was effective in 88%. Three of the four successful devices were also 100% effective in experiment II; the fourth was effective in 75%. Failure of tourniquets to eliminate distal Doppler pulse signal was due to inadequate mechanical advantage for tightening, device failure (breakage), or intolerable pinching or circumferential pain prior to pulse elimination. The Combat Application Tourniquet (North American Rescue Products, Inc.), the Emergency & Military Tourniquet (Delfi Medical Innovations, Inc.), and the Special Operations Forces Tactical Tourniquet (Tactical Medical Solutions, LLC) were all found to be 100% effective in elimination of distal arterial pulse in both the arm and the leg in all subjects. CONCLUSION: Some commercially available tourniquets do not reliably occlude arterial blood flow and may not be successful in preventing extremity exsanguination in a trauma patient. Potential purchasers of such devices should bear this in mind when selecting a device for clinical use.